For switching off a load completely, the best solution is, to disconnect the input voltage. Then the load is in a safe mode and does not have any power consumption. For disconnecting an input supply voltage to a load, for example a relay can be used as a switch. But most of the relays are not designed for the operation of a high DC voltage, for example 400 Volts, and for high power loads above 200 Watts. Therefore, a standard relay cannot be used, which makes this solution rather expensive.
For switching a DC supply voltage to a load, also a switching transistor can be used, for example a MOSFET. The switching transistor can be coupled for example on the high side between the DC supply voltage and a first input terminal of the load, and the second input terminal of the load being coupled to ground. Or in a second embodiment, the switching transistor is coupled between the load and ground, and an input terminal of the load is coupled directly to the DC supply voltage. In case a high power capacitive load is used, the switching transistor has to handle rather high switching losses, when the load is switched on.